1. Field of the Invention
The present specification relates generally to charging in communication networks. The present specification also relates generally, but not exclusively; to third generation (Universal Mobile Telecommunication System UMTS) networks.
2. Description of the Related Art
A communication system generally refers to a facility that enables communication between two or more entities such as user terminal equipment and/or network entities and other nodes associated with a communication system. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on.
The communication may be provided by a fixed line and/or wireless communication interfaces. A feature of some wireless communication systems is that they provide mobility for the users thereof. An example of communication systems providing wireless communication is a public land mobile network (PLMN). An example of the fixed line system is a public switched telephone network (PSTN).
A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of a system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched server or a packet switched server or both. Communication protocols and/or parameters which are preferably used for the connection are also typically defined. For example, the manner of how communication shall be implemented between the user equipment and the elements of the communication networks is typically based on a predefined communication protocol. In other words, a specific set of “rules” on which the communication may be based on is preferably defined to enable the user equipment to communicate via the communication system.
The introduction of Third Generation (3G) communication systems will, in all likelihood, significantly increase the possibilities for accessing services on the Internet via mobile user equipment (UE) as well as other types of UE.
Various user equipment (UE) such as computers (fixed or portable), mobile telephones, personal data assistants or organisers and so on are known to the skilled person and can be used to access the Internet to obtain services. Mobile user equipment, typically referred to as a mobile station (MS), can be defined as a means that is capable of communication via a wireless interface with another device such as a base station of a mobile telecommunication network or any other station.
The term “service” used above and hereinafter will generally be understood to broadly cover any service or goods which a user may desire, require or be provided with. The term also will generally be understood to cover the provision of complimentary services. In particular, but not exclusively, the term “service” will be understood to include Internet protocol multimedia IM services, conferencing, telephony, gaming, rich call, presence, e-commerce and messaging, for example, instant messaging.
The 3G Partnership Project (3GPP) is defining a reference architecture for the Universal Mobile Telecommunication System (UMTS) core network which will, in all likelihood, provide the users of user equipment (UE) with access to these services. This UMTS core network is divided into three principal domains. These are the Circuit Switched domain, the Packet Switched domain and the Internet Protocol Multimedia (IM) domain.
The latter of these, the IM domain, typically makes sure that multimedia services are adequately managed. The IM domain typically supports the Session Initiation Protocol (SIP) as developed by the Internet Engineering Task Force (IETF).
SIP is an application layer signalling protocol for starting, changing and ending user sessions as well as for sending and receiving transactions. A session may, for example, be a two-way telephone call or multi-way conference session or connection between a user and an application server (AS). The establishment of these sessions generally enables a user to be provided with the above-mentioned services. One of the most commonly included features of SIP is that the protocol typically enables personal mobility of a user using mobile UE by providing the capability to reach a called party (which can be an application server AS) or another user equipment via a single location independent address.
A user connected to SIP based communication system may generally communicate with various entities of the communication system based on standardised SIP messages. SIP is typically defined in an Internet Engineering Task Force (IETF) protocol specification by G Rosenberg et al., titled: “SIP: session initiation protocol” RFC 3261, July 2001. This document is herein incorporated by reference in its entirety.
One version of the third generation standard is “release 5” or “rel5”. This introduces the IP multimedia core network subsystem that has been developed to use SIP technology as a basis for all IP services such as voice over IP, amongst others. The SIP standard is a rendezvous protocol which typically may be used to establish media sessions between a SIP user agent client (UAC) and a SIP user agent server (UAC). To open a session, SIP generally uses the SDP (session description protocol) protocol and it is thus possible to establish a variety of sessions, depending on the used application both for real time services and non real time services. The SIP is generally a flexible protocol that can be used to establish different type of sessions. For example, some sessions may require a certain precondition to be satisfied. Other sessions may require reliable provisional responses. Other sessions may require confirmation of reserved resources. It is also possible to have a variable number of SDP offer/answer exchanges.
In order to enable charging correlation at the media component level for charging events related to the same SIP session and generated in different domains (i.e. access network and IM subsystem (IMS) network) for the same SIP session, the access network charging identifier identifying the resource reservation carrying a particular media flow (e.g. in GPRS (general packet radio service) access the GPRS Charging Identifier and GGSN (gateway GPRS support node) address) is preferably to be sent and distributed in the IMS network. This access charging identifier is typically sent to P-CSCF (PDF) (proxy call session control function and policy decision function respectively) via the Go interface and distributed in IMS in a SIP “UPDATE” message. With the next version which has been proposed for the 3GPP standard, “release 6” or “rel6” it is possible that for some session set up scenarios an UPDATE message is not sent at all. This generally results in the problem that the network is unable to distribute the charging identifier between the network elements that require this information.
In the current proposals for release 5, the UPDATE request is typically sent from the user equipment to the P-CSCF. A confirmation of the preconditions are commonly requested in a response when the user equipment finishes a quality of service reservation for both the up link and down link directions. The calling party generally sends the UPDATE request to the terminating end point via the signalling path established by the INVITE request. The UPDATE request frequently includes in the SDP, the information about the successful quality of service bi-directional mode, due to the successful bi-directional PDP context established. The SDP generally indicates that the quality of service resource reservation for both send and receive mode was successful from the terminating end point side.
With the proposals for release 6, for example, it is possible that a session can be established by a simple SIP INVITE/200 OK transaction or it is possible that the end points involved in the session set up will not make use of preconditions or not ask for confirmation of reserved resources. In all of these cases, the UPDATE message will typically not be sent and thus distribution of the charging identity is generally not possible.